RFID technology generally involves interrogating an RFID tag with radio frequency (RF) waves and reading the responding RF waves with a RFID reader. A RFID tag typically includes a miniscule microchip coupled to an RF antenna. RFID tags can be attached to the object to be identified. An RFID reader typically includes an antenna coupled to a transmitter and a receiver.
In some implementations the antenna in the RFID reader can generate RF waves with different polarizations. For example, as shown in FIG. 1A-FIG. 1C, the RFID reader 40 can generate RF waves in x-polarization, y-polarization, or circular polarization, for interrogating an RFID tag 60. Many RFID tags mainly respond to the interrogating RF waves with one particular polarization. For example, as shown in FIG. 1A-FIG. 1C, when the RFID tag 60 mainly responds to the interrogating RF waves with x-polarization, it can be characterized that the RFID tag is linear polarized and has the orientation in the x-direction. In FIG. 1A, when the RFID reader 40 generates the interrogating RF waves with x-polarization, generally, some of these x-polarized RF waves can be efficiently coupled to the antenna of the RFID tag 60. In FIG. 1B, when the RFID reader 40 generates the interrogating RF waves with y-polarization, generally, it can be difficult for these y-polarized RF waves to be efficiently coupled to the antenna of the RFID tag 60. In FIG. 1C, when the RFID reader 40 generates the interrogating RF waves with circular polarization, only the x-component of the circular polarization can possibly be efficiently coupled to the antenna of the RFID tag 60.
Generally, depending upon how an RFID tag is attached to an object and how the object changes its orientation after the attachment, an operator of the RFID reader may not always know the orientation of the RFID tag. If the orientation of the RFID tag is in the x-direction, the operator of the RFID reader may want to generate the interrogating RF waves with x-polarization to maximize the RF power received by the RFID tag. If the orientation of the RFID tag is in the y-direction, the operator of the RFID reader may want to generate the interrogating RF waves with y-polarization. If the orientation of a linear polarized RFID tag is unknown, the operator of the RFID reader can generate the interrogating RF waves with circular polarization. With the circular polarization, however, at least half of the RF power of the interrogating RF waves is not coupled to the linear polarized RFID tag.
It is desirable to have an RFID reader that can adapt to its application and environment by configuring itself to operate in a mode that may improve its performance.